GK MB115 only works cranked...

My friend bought a GK MB115 and he loves the amp but it just has this one issue :

It will only work if the master volume is cranked all the way. There is no output at all until you reach the very end of the master volume knob, regardless of where the gain knob is.
So the only way he can use it is by controlling his volume with the gain and have the master cranked all the way but that also triggers the thermal protection afer a while since the power section is always cranked...

I understand this is a digital amp. It feels like a component isn't turning on or letting the signal through until it reaches a certain threshold on the power amp. The master volume knob isn't dirty or scratchy, it's just dead quiet until you reach about 90% of the range.

I've already unplugged and re-plugged all the internal connectors and also sprayed and cleaned all the pots and switches.
Everything works fine (all inputs and controls) except for this master volume issue.
Not really sure what the next step to troubleshoot would be except maybe changing the master volume pot ???

Appreciate the quick answers !
munkeyfish, Amp is not new so returning to GK isn't really an option.
mmbongo, I already cleaned the pots and switches out with contact/tuner cleaner, without spraying everything of course !
I fix and mod tube amps all the time so I have experience with that but rarely work on solid state amp. I have a multimeter and most other tools. I assumed it was digital because of how recent it is... My mistake !
I'll send an email to GK to see what they say.
Any suggestions other than sending the amp to GK ?

Good chance the pot wiper is hanging up internally, really changing the pot is the only way if that's the issue.
If you are handy with such things you can disconnect the pot from the circuit & test the resistance with a meter.

Level and Master Volume settings: Set the
master volume to 12 o'clock. (MB210, MB115,
MB410 and MB212 only) While playing, turn
the input gain up to the desired volume level.
At this point you can experiment with different
EQ, contour, horn and boost settings.

Appreciate the quick answers !
munkeyfish, Amp is not new so returning to GK isn't really an option.
mmbongo, I already cleaned the pots and switches out with contact/tuner cleaner, without spraying everything of course !
I fix and mod tube amps all the time so I have experience with that but rarely work on solid state amp. I have a multimeter and most other tools. I assumed it was digital because of how recent it is... My mistake !
I'll send an email to GK to see what they say.
Any suggestions other than sending the amp to GK ?

Click to expand...

doesn’t matter if the amp is new or not, they’ll still fix it, albiet not for free

My friend bought a GK MB115 and he loves the amp but it just has this one issue :

It will only work if the master volume is cranked all the way. There is no output at all until you reach the very end of the master volume knob, regardless of where the gain knob is.
So the only way he can use it is by controlling his volume with the gain and have the master cranked all the way but that also triggers the thermal protection afer a while since the power section is always cranked...

I understand this is a digital amp. It feels like a component isn't turning on or letting the signal through until it reaches a certain threshold on the power amp. The master volume knob isn't dirty or scratchy, it's just dead quiet until you reach about 90% of the range.

I've already unplugged and re-plugged all the internal connectors and also sprayed and cleaned all the pots and switches.
Everything works fine (all inputs and controls) except for this master volume issue.
Not really sure what the next step to troubleshoot would be except maybe changing the master volume pot ???

Thanks,

Bluezmax

Click to expand...

While all the above suggestions are your mostly likely course of action, consider that you may have an "intermittent" connection somewhere in the signal path that only works when the gain is turned up.

Example: I was using a pair of Klipschorns (extremely efficient speaker systems) with a high power Crown power amp and pre amp. At the time Klipsch recommended using a fuse between the power amp and speaker. The system developed an issue where one of the speakers would not play unless I turned the pre amp volume up to a certain point (as in way to too loud). So naturally I assumed the problem was in the pre amp. It actually turned out to be a hairline crack in the speaker cable fuse holder. The crack was just enough to let some tension off the spring loaded fuse so that it would not make a connection - unless - the gain was turned up enough where the current/voltage could "jump the gap". Removed the fuse/fuse holder and everything worked fine. In your case this could be caused by faulty jack, internal jack wire on the amp or speaker cabinet etc.

My friend bought a GK MB115 and he loves the amp but it just has this one issue :

It will only work if the master volume is cranked all the way. There is no output at all until you reach the very end of the master volume knob, regardless of where the gain knob is.
So the only way he can use it is by controlling his volume with the gain and have the master cranked all the way but that also triggers the thermal protection afer a while since the power section is always cranked...

I understand this is a digital amp. It feels like a component isn't turning on or letting the signal through until it reaches a certain threshold on the power amp. The master volume knob isn't dirty or scratchy, it's just dead quiet until you reach about 90% of the range.

I've already unplugged and re-plugged all the internal connectors and also sprayed and cleaned all the pots and switches.
Everything works fine (all inputs and controls) except for this master volume issue.
Not really sure what the next step to troubleshoot would be except maybe changing the master volume pot ???

Thanks,

Bluezmax

Click to expand...

maybe you can clean the volume pot … but probably this is a worse problem that will get worse and not better

This is why people should have 2 bass heads … because sometimes one will die

Thanks for all the replies.
I did send an email to GK asking if they believe the pot replacement is the correct fix.
I've already located the correct pot and am about to order it. Changing a circuit board mounted pot is child's play for me. I've had to redo entire burnt out boards from some tube amps, even redoing some of the burnt traces...
I will take a closer look to look for any intermittent connections as Artto suggested as well.
I really believe it's a damaged pot since there are no noises as you crank the master volume pot until you reach the 90% travel point. And when putting sound out, it is clear, undistorted and just sounds great.

Thanks for all the help. I will give an update once the new pot is in.